In a large mixing bowl, combine the flour, salt, and 1 tablespoon of sugar. Add the butter and break it up with your fingers, mixing it in with the flour mixture.
Add in 2 tablespoons of cold water and begin mixing the dough all together. If it needs more water, add a tiny bit more in, until it forms a crust consistency. Bring the dough into a ball shape, cover and refrigerate for 20 minutes.
After 20 minutes, take the dough out and place it on a cutting board that is lightly floured. Begin to knead the dough gently, forming it into a rectangle, keeping the edges even. Try to make sure you still have some flecks of butter visible in the dough.
Fold the top third of the dough down to the center, then the bottom third up and over that. Roll the dough out again, turning it vertically so that it reaches three times its length. Fold it in thirds again, cover and put in the refrigerator for 30 minutes.
While the dough is resting, you can make the custard filling! Dissolve 1/2 cup of sugar into the hot water, in a large mixing bowl. Allow this to cool to room temperature. Thoroughly whisk eggs and evaporated milk together in a separate bowl and then whisk in the sugar water and vanilla.
Strain your egg mixture through a mesh strainer in order to get your mixture to a smooth consistency without bubbles. Preheat your oven to 400 degrees.
Roll out the dough and cut circles to fit your small aluminum tart tins. Press your dough into the tins to fill each one. Then fill them with the egg mixture, 3/4 of the way to the top. Place all of your tins onto a baking sheet and pop them in the oven!
Bake them for 15 minutes, reducing the temperature to 350 degrees and baking again for another 10-12 minutes, until the filling is just set. Let the tarts cool for a couple of minutes and enjoy them while they are warm!